Fluid emitting devices, particularly for irrigation systems are known. For example U.S. Pat. No. 4,428,397 describes a device of this type.
However, the above mentioned devices have some drawbacks. The adjustment of the flow rate in relation to the pressure difference between the two chambers divided by the membrane is solely obtained by means of structural and elasticity properties of the membrane. Therefore, the membrane is the only functional member determining the adjustment for a very large range of pressure differences.
Besides a saturation effect, i.e. a non-response effect when the fluid pressure difference in the two chambers divided by the membrane is over a certain maximum limit value and when it is lower than a certain minimum value, the continuous elastic stress of the material composing the membrane can cause the ageing of the material with regard to elastic characteristics and it may not be possible to adjust pressure difference values close to extreme values of the pressure difference range, within which the elastic behavior of the membrane would guarantee the flow rate to be adjusted. For example, when the membrane has to operate for a long time under high pressure difference conditions, the material can be inelastically deformed or stretched and so the elastic recovery to the original configuration cannot occur, rendering impossible the adjustment upon a low pressure difference.
Moreover, in order to guarantee a lasting and optimal elastic behavior, the membrane has to be composed of a material with high elastic qualities and so quite expensive. This has a considerable effect as regards total costs of irrigation systems having a large number of said emitters.
In FR 1.299.719, a flow regulating device is disclosed that includes two chambers separated by a membrane. One of the two chambers communicates with an inlet duct for a pressure fluid and the other one communicates with a duct delivering said pressure fluid, with the fluid passing from a chamber to the other one via a through aperture provided in said membrane. An outlet spout cooperates with the membrane for defining a predetermined pressure in the corresponding chamber of the device that communicates with the delivering duct, which outlet spout can be adjusted with reference to its relative position with respect to the membrane.
In such device, the distance between the membrane and the outlet spout acts for allowing a pressure to be adjusted on the corresponding side of the membrane, but it does not allow a range of the flow rate to be adjusted. Moreover the membrane has to be perforated thus making it highly sensitive to wear and so it is subjected to breaking or to functionality loss.
In all known devices, the flow rate is adjusted by limiting and controlling the pressure. After all known devices do not act independently of the flow rate and pressure. The two magnitudes can be really correlated one with the other. However there is the need of independently adjusting the two magnitudes, at least as regards a certain range of pressures and/or flow rates.